On top of the words ut'shuvah utefila utzedakah1 in most machzorim it also says Zom, Kol, Mamon2.

Why zom on teshuvah if the Rambam's formula for teshuva (Hl. Teshuva 2) no mention of fasting; why not vidui azivas hachet etc., instead?
Why kol (voice) by utefila when you can also have tefila belachash (quietly)?
Why mamon by zedakah?

1: And Repentance, and Prayer, and Charity [removes the severity of the decree]2: Fasting, Voice, Money

2 Answers
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The Sefer HaMinhagim of R' Yitzchak Tyrnau notes that all three words have the same gematria of 136; this is to remind us that all three aspects are equally important (Hagahos haMinhagim Aseres Y'mei Teshuvah). The Chasam Sofer notes that these three elements were employed by the people of Ninveh in their efforts to achieve divine pardon, and this set the precedent for future generations (Commentary to perek Arvei Pesachim).

The Maharil also notes the gematrias. The reason is that during the middle ages, a question arose as to why the author of the piyut deviated from the order of the 3 actions as stated in the Talmud Bavli (I don't have the source or quote handy). Some tried to change the order around in order to match the Talmudic sources and others felt the need to preserve the text of the piyut as they had it. The point made by those gematrias is that, in fact, all three actions are equal and they shouldn't change the order.